Comparative Ecology of Notropis albeolus, N. ardens and N. cerasinus (Cyprinidae) in the Upper Roanoke River Drainage, Virginia

Abstract

Foods, feeding periodicity and microhabitat use are reported for coexisting Notropis albeolus, N. ardens and N. cerasinus in the upper Roanoke River drainage, Virginia. All three species primarily occupied pool habitats, ate aquatic insect larvae or terrestrial adult insects, and were diurnal feeders. Notropis ardens (subgenus Lythrurus) was ecologically segregated from N. albeolus and N. cerasinus (both subgenus Luxilus) in vertical spacing in the water column and in taxa of foods used. The two Luxilus species were ecologically more similar, segregated only by vertical differences in microhabitat. Overlaps in resource use among the three species pairs suggested congruence of phylogenetic and ecological similarities. INTRODUCTION The phenomenon of resource partitioning is well-documented in reptile, bird and mammal communities (cf., Pianka, 1973; Schoener, 1974), and in numerous freshwater fish communities closely related, coexisting species differ ecologically, e.g., in microhabitat, food or feeding chronology (Hartley, 1948; Keast, 1965, 1966, 1978; Zaret and Rand, 1971; Werner and Hall, 1976, 1979; Werner et al., 1977). It has often been assumed that some segregation in resource use is a requisite for coexistence of species, and that observed ecological differences among coexisting taxa result from past or present competitive interactions. However, uncritical acceptance of a competition model to account for ecological differences among coexisting fish species may be unwarranted (Sale, 1979), and the plausibility of alternative hypotheses should be considered. Mendelson (1975), for example, suggested that coexisting minnows used resources in patterns set by morphological preadaptation. In eastern North America, minnows of the genus Notropis (Cyprinidae) often occur in multispecies aggregations, using habitats and foods that superficially appear similar. However, Starrett (1950), Whitaker (1977), Gillen and Hart (1980) and Hoover (1981) showed trophic segregation among coexisting Notropis species, and Moyle (1973) and Baker and Ross (1981) demonstrated that coexisting Notropis species segregated vertically into different microhabits. Mendelson (1975) showed that four coexisting Notropis were ecologically segregated more by use of space than by diet. While these studies suggest the importance of dietary and microhabitat segregation among coexisting Notropis, there has been too little comparative research within this diverse genus (at least 119 species) to permit generalization about mechanisms that facilitate species coexistence. In this study we evaluate ecological segregation among three syntopic Notropis species, with emphasis on microhabitat, food and feeding chronology in a complex upland stream system. We also provide information on cold vs. warm weather ecology of the species. Our study focuses on Notropis albeolus (white shiner, subgenus Luxilus), N. ardens (rosefin shiner, subgenus Lythrurus) and N. cerasinus (crescent shiner, subgenus Luxilus), which are the three most common Notropis in the upper Roanoke River drainage above Salem, Virginia (Jordan, 1889; Cairns et al. 1971; Jenkins, 1979). All three coexist in the river mainstream and in larger tributaries, but N. cerasinus occurs somewhat further 'Address reprint requests to Matthews.